U.S. patent application number 09/983518 was filed with the patent office on 2002-06-27 for solid polymer electrolyte membrane and fuel cell comprising same.
This patent application is currently assigned to HONDA GIKEN KOGYO KBUSHIKI KAISHA. Invention is credited to Kimura, Nobuaki, Suenaga, Toshihiko.
Application Number | 20020081476 09/983518 |
Document ID | / |
Family ID | 18802001 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081476 |
Kind Code |
A1 |
Suenaga, Toshihiko ; et
al. |
June 27, 2002 |
Solid polymer electrolyte membrane and fuel cell comprising
same
Abstract
A solid polymer electrolyte membrane comprising a base film and
a moisture-proof layer. The moisture-proof layer may be disposed on
an outer edge portion of the base film. The solid polymer
electrolyte membrane according to an embodiment of the present
invention is for use in a fuel cell, and comprises the base film
having an electricity-generating region and a
non-electricity-generating region, and the moisture-proof layer
disposed on at least a part of the non-electricity-generating
region. A fuel cell using the solid polymer electrolyte membrane is
also provided.
Inventors: |
Suenaga, Toshihiko;
(Saitama-ken, JP) ; Kimura, Nobuaki; (Saitma-ken,
JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
Suite 600
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Assignee: |
HONDA GIKEN KOGYO KBUSHIKI
KAISHA
|
Family ID: |
18802001 |
Appl. No.: |
09/983518 |
Filed: |
October 24, 2001 |
Current U.S.
Class: |
429/465 ;
429/309 |
Current CPC
Class: |
H01M 8/0271 20130101;
H01M 8/1023 20130101; Y02E 60/50 20130101; H01M 8/1053 20130101;
H01M 8/1065 20130101; H01M 8/0273 20130101; H01M 8/1039
20130101 |
Class at
Publication: |
429/33 ; 429/35;
429/309 |
International
Class: |
H01M 008/10; H01M
008/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2000 |
JP |
2000-324478 |
Claims
What is claimed is:
1. A solid polymer electrolyte membrane comprising a base film and
a moisture-proof layer disposed on an outer edge portion of said
base film.
2. The solid polymer electrolyte membrane according to claim 1,
wherein said base film is made of a perfluorinated sulfonic acid
polymer and said moisture-proof layer is made of a fluororesin.
3. The solid polymer electrolyte membrane according to claim 1,
wherein said moisture-proof layer is formed by applying a
cold-setting type moisture-proof material to said base film.
4. The solid polymer electrolyte membrane according to claim 1,
wherein said moisture-proof layer is formed by a method selected
from the group consisting of coating methods, spray methods,
dipping methods and printing methods.
5. A solid polymer electrolyte membrane for use in a fuel cell,
wherein said solid polymer electrolyte membrane comprises a base
film having an electricity-generating region and a
non-electricity-generating region, and a moisture-proof layer
disposed on at least a part of said non-electricity-generating
region.
6. The solid polymer electrolyte membrane according to claim 5,
wherein said solid polymer electrolyte membrane is used in a fuel
cell such that said non-electricity-generating region is sandwiched
between a couple of sealing frames, said moisture-proof layer being
disposed between said non-electricity-generating region and each of
said sealing frames.
7. The solid polymer electrolyte membrane according to claim 5,
wherein said base film is made of a perfluorinated sulfonic acid
polymer and said moisture-proof layer is made of a fluororesin.
8. The solid polymer electrolyte membrane according to claim 5,
wherein said moisture-proof layer is formed by applying a
cold-setting type moisture-proof material to said base film.
9. The solid polymer electrolyte membrane according to claim 5,
wherein said moisture-proof layer is formed by a method selected
from the group consisting of coating methods, spray methods,
dipping methods and printing methods.
10. A fuel cell comprising a plurality of fuel cell units stacked
with each other and a separator disposed between said fuel cell
units, wherein each of said fuel cell units comprises an anode, a
cathode and the solid polymer electrolyte membrane recited in claim
1 or 5 disposed between said anode and said cathode.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a solid polymer electrolyte
membrane usable for a solid polymer electrolyte fuel cell (PEFC),
particularly to a solid polymer electrolyte membrane that is
excellent in sealing properties to be capable of preventing leakage
of a fuel gas (hydrogen gas), an oxidant gas (air), a
humidification water and a coolant in a fuel cell. The present
invention also relates to a fuel cell comprising the solid polymer
electrolyte membrane.
[0002] In general, a fuel cell is provided by stacking a plurality
of fuel cell units, a separator being disposed between the fuel
cell units. Each of the fuel cell units comprises a solid polymer
electrolyte membrane, an anode disposed on one surface of the
membrane, and a cathode disposed on another surface of the
membrane. More specifically, such a stacked-type fuel cell
comprises: a carbon separator with electron-transporting properties
having passages for independently introducing a fuel gas, an
oxidant gas and a coolant to each fuel cell unit; a carbon fiber
diffusion layer that diffuses the fuel gas or the oxidant gas and
comes into contact with a convex part of the carbon separator to
transfer electrons between an electrode and the carbon separator;
an anode where the fuel gas is subjected to a chemical reaction to
provide protons and electrons; a cathode where water is generated
from oxygen, protons and electrons; and an electrolyte membrane in
a wet state for transporting protons.
[0003] The fuel gas and the oxidant gas are used for the fuel cell
as reaction gases, the fuel gas is supplied through an anode side
passage of the separator, and the oxidant gas Is supplied through a
cathode side passage of the separator. When each fuel cell unit is
supplied with the reaction gases, the electrochemical reaction
proceeds to generate electrons and the electrons are utilized in an
external circuit as an electric energy.
[0004] The fuel gas, the oxidant gas and the coolant should be
independently supplied to the fuel cell unit through different
passages, therefore, it is important to seal the passages. Sealing
method can be selected from various methods depending on the
structure of the stacked fuel cell units. For example, a sealant
may be disposed: around a communicating aperture going through the
fuel cell stack for supplying the fuel gas, the oxidant gas, the
humidification water and the coolant to each fuel cell unit; on the
periphery of MEA (the electrolyte membrane+the electrodes+the
diffusion layer); on the periphery of the passage where the coolant
is supplied along surfaces of the separator to cool the separator;
on the periphery of the separator; etc.
[0005] Known as the sealing method are: (i) methods where the fuel
cell units and a frame having a sheet-shape, an O-shape, etc. are
stacked while pressing, the frame being made of an elastic material
such as an organic rubber (a fluoro-rubber, a silicone rubber,
ethylene-propylene rubber, etc.) and an adhesive If hardening
type-liquid material, thereby utilizing repulsive force of the
elastic material to seal the fuel cell; (ii) methods where the fuel
cell is compressed and sealed by an inorganic sheet such as a fiber
sheet of graphite, ceramic, etc.; (iii) methods using a caulking or
a mechanical sealant; etc.
[0006] Though a material for the sealant and a shape of the sealant
should be selected in accordance with strength, surface state, etc.
of the separator or MEA, the sealant is preferably miniaturized in
the case of equipping an automobile with the fuel cell. In
particular, each fuel cell unit of the fuel cell has to be thinned,
thus, MEA and the separator have to be thinned. The separator, with
which the sealant directly comes into contact, is generally made of
a brittle material such as carbon, etc., so that the thinned
separator is often broken when it is stacked with the fuel cell
units. Thus, among the above methods of (i), (ii) and (iii),
preferred are the methods of (i) using the sealant having proper
elasticity and repellency.
[0007] However, when the fuel cell units and the separator are
sufficiently sealed while pressing such that the separator is not
broken, surface states such as a crease, a swell, a fold, a bend, a
roughness, etc. of the MEA, particularly the electrolyte membrane
coming into contact with the sealant, is remarkably affecting the
sealing properties.
[0008] The electrolyte membrane in MEA is disadvantageous in that
it abruptly expands or shrinks correspondingly to moisture content
of air. The portion of MEA that comes in contact with the sealant
is composed of only the electrolyte membrane without the electrodes
and the diffusion layer, and the electrolyte membrane is often
creased by the sealant. Thus, it is difficult to secure sufficient
sealing properties even if the material and structure of the
sealant are properly selected. Further, strict humidity control is
required to assemble the MEA into the fuel cell without creasing
the electrolyte membrane, thus, the conventional sealed fuel cells
are poor in productivity.
OBJECT AND SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide a solid
polymer electrolyte membrane, which is easily handled without
strict humidity control, and which provides sufficient gas-sealing
properties with a separator in a fuel cell. Another object of the
present invention is to provide a fuel cell comprising the solid
polymer electrolyte membrane.
[0010] As a result of intense research in view of the above
objects, the inventor has found that a solid polymer electrolyte
membrane comprising a particular moisture-proof layer does not
abruptly expand or shrink correspondingly to moisture content of
air, can be handled with ease, and does not affect
electricity-generating properties of a fuel cell. The present
invention has been accomplished by the finding.
[0011] Thus, the solid polymer electrolyte membrane of the present
invention comprises a base film and a moisture-proof layer disposed
thereon. The moisture-proof layer may be disposed on an outer edge
portion of the base film.
[0012] The solid polymer electrolyte membrane of the present
invention may be used in a fuel cell. In this case, the solid
polymer electrolyte membrane comprises the base film and the
moisture-proof layer, the base film has an electricity-generating
region and a non-electricity-generatin- g region, and the
moisture-proof layer is disposed on at least a part of the
non-electricity-generating region. The electricity-generating
region of the base film is sandwiched between an anode and a
cathode of the fuel cell. The non-electricity-generating region is
such a region on which power generation is not carried out, and is
generally an outer edge portion of the base film. Thus, in the
solid polymer electrolyte membrane of the present invention, the
moisture-proof layer is disposed on the non-electricity-generating
region to prevent the solid polymer electrolyte membrane from
expanding, shrinkage and creasing owing to moisture in air. As a
result, a sealing surface of the solid polymer electrolyte membrane
is improved with respect to smoothness, whereby the solid polymer
electrolyte membrane is excellent in sealing properties.
[0013] The solid polymer electrolyte membrane of the present
invention may be entirely made of a solid polymer. In this case,
differences of expanding characteristics and shrinking
characteristics are remarkably slight between the
electricity-generating region and the non-electricity-generating
region, whereby stress is hardly generated in the solid polymer
electrolyte membrane. Further, mechanical strength of the solid
polymer electrolyte membrane is improved by the moisture-proof
layer. The solid polymer electrolyte membrane is hardly broken even
if it is exposed out of the electrodes and the diffusion layer,
whereby it hardly protrudes over the communicating aperture. When
the solid polymer electrolyte membrane of the present invention is
used in a fuel cell, it is preferable that the
non-electricity-generating region is sandwiched between a couple of
sealing frames and that the moisture-proof layer is disposed
between the non-electricity-generating region and the sealing
frames.
[0014] In the solid polymer electrolyte membrane of the present
invention, it is preferred that the base film is made of
perfluorinated sulfonic acid polymer and the moisture-proof layer
is made of a fluororesin. The moisture-proof layer is preferably
formed by applying a cold-setting type moisture-proof material to
the base film. A method for forming the moisture-proof layer is
preferably selected from the group consisting of coating methods,
spray methods, dipping methods and printing methods.
[0015] A fuel cell of the present invention comprises a plurality
of fuel cell units stacked with each other and a separator disposed
between the fuel cell units, each of the fuel cell units comprising
an anode, a cathode and the solid polymer electrolyte membrane of
the present invention disposed between the anode and the
cathode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1(a), 1(b) and 1(c) are a schematic, top view showing
an example of a solid polymer electrolyte membrane according to the
present invention, respectively;
[0017] FIG. 2 is a schematic, cross-sectional view showing an
example of a fuel cell according to the present invention where
solid polymer electrolyte membranes of the present invention are
assembled with separators;
[0018] FIGS. 3(a) and 3(b) are schematic views showing production
of a solid polymer electrolyte membrane of the present invention;
and
[0019] FIG. 4 is a schematic, cross-sectional view showing an
apparatus used for a sealing properties test in EXAMPLES.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] A solid polymer electrolyte membrane of the present
invention comprises a base film and a moisture-proof layer disposed
on at least a part of the base film. The moisture-proof layer may
be disposed on an outer edge portion of the base film.
[0021] The solid polymer electrolyte membrane of the present
invention may be used in a fuel cell. In this case, the solid
polymer electrolyte membrane comprises the base film and the
moisture-proof layer, the base film has an electricity-generating
region and a non-electricity-generatin- g region, and the
moisture-proof layer is disposed on at least a part of the
non-electricity-generating region. The electricity-generating
region is sandwiched between an anode and a cathode of the fuel
cell, thereby being such a region where a cell reaction is carried
out. The non-electricity-generating region is not sandwiched
between the anode and the cathode, and thereon is not carried out
power generation. The solid polymer electrolyte membrane of the
present invention comprises the moisture-proof layer to more
effectively sealing the fuel cell without decreasing
electricity-generating ability of the fuel cell.
[0022] Material used for the base film is not particularly limited
if only it has conductivity to protons and electrons generated by
an electrochemical reaction. The base film may be made of a polymer
such as a fluorine-containing polymer, a hydrocarbon polymer, a
polymer impregnated with phosphoric acid, etc. The base film is
preferably made of an electro-conductive polymer of perfluorinated
sulfonic acid such as "Nafion 117" from the viewpoint of thinning
the solid polymer electrolyte membrane. The thickness of the base
film is preferably 10 to 80 .mu.m, more preferably 15 to 50
.mu.m.
[0023] The moisture-proof layer is made of a moisture-proof
material, which is not particularly limited and may be known
material. From the viewpoint of adhesion between the base film and
the moisture-proof layer, it is preferred that the moisture-proof
layer is mainly made of the moisture-proof material similar to the
material used for the base film, thus, it is preferable that the
materials each used for the moisture-proof layer and the base film
has high compatibility. For example, in the case where the base
film is made of perfluorinated sulfonic acid polymer, it is
preferable that the moisture-proof material is composed of a
fluororesin. Further, a component that can increase adhesive
properties between the moisture-proof layer and the following
sealing frame is preferably added to the moisture-proof
material,
[0024] The moisture-proof material is preferably such a
cold-setting type moisture-proof material that can be hardened
without heating. The moisture-proof material may be dissolved in an
organic solvent, water, etc. The moisture-proof material may be a
heat-setting type moisture-proof material if the material can be
hardened at a temperature, deterioration of the base film being not
caused by the effect of the temperature.
[0025] In this invention, the moisture-proof layer of the
moisture-proof material is formed on at least a part of the solid
polymer electrolyte membrane to prevent the membrane from moisture
absorption. Thickness of the moisture-proof layer is preferably 1
to 30 .mu.m, particularly preferably 3 to 10 .mu.m Though the
moisture-proof layer may be disposed on only one side of the base
film, it is preferred on the both sides of the base film is
disposed the moisture-proof layers.
[0026] A fuel cell of the present invention comprises a plurality
of fuel cell units stacked with each other and a separator disposed
between the fuel cell units. Each of the fuel cell units comprises
an anode and a cathode, and the above-mentioned solid polymer
electrolyte membrane of the present invention disposed
therebetween. In the fuel cell of the present invention, though the
moisture-proof layer is disposed on any position of the base film,
the non-electricity-generating region is generally located on an
outer edge portion of the base film, whereby the moisture-proof
layer is disposed on the outer edge portion. It is preferable that
the non-electricity-generating region is sandwiched between a
couple of sealing frames and the moisture-proof layer is disposed
between the non-electricity-generating region and the sealing
frames.
[0027] FIGS. 1(a), 1(b) and 1(c) are a schematic, top view showing
an example of a solid polymer electrolyte membrane according to the
present invention, respectively. In the solid polymer electrolyte
membrane shown in FIG. 1(a), the non-electricity-generating region
is located on the outer edge portion of the square base film, and
the moisture-proof layer 11 is disposed on the entire
non-electricity-generating region. On the electricity-generating
region 13 shown with a dotted line is located the anode and the
cathode. The non-electricity-generating region is not required to
be entirely covered with the moisture-proof layer, and the
non-electricity-generating region may be partially exposed. For
example, in the solid polymer electrolyte membrane shown in FIG.
1(b), the non-electricity-generating region comprises: an end part
where the moisture-proof layer is disposed; and a middle part that
is not subjected to a treatment with the moisture-proof material.
Further, as shown in FIG. 1(c), the electricity-generating region
may be partly covered with the moisture-proof layer if the layer
does not act to decrease the electricity generating properties of
the fuel cell.
[0028] Although each of the solid polymer electrolyte membranes
shown in FIGS. 1(a), 1(b) and 1(c) is in shape of a square, the
shape of the solid polymer electrolyte membrane is not limited. In
the case where a communicating aperture goes through the fuel cell
stack for supplying the fuel gas, etc. to each fuel cell unit, the
solid polymer electrolyte membrane may have an opening
correspondingly to the communicating aperture. Further, the
position, on which the moisture-proof layer is disposed, is also
not limited to the outer edge portion of the base film. For
example, in the case where the opening corresponding to the
communicating aperture is disposed on a portion other than the
outer edge portion, the moisture-proof layer may be disposed around
the opening.
[0029] FIG. 2 is a schematic, cross-sectional view showing an
example of a fuel cell according to the present invention where
solid polymer electrolyte membranes 1 of the present invention are
assembled with separators 22. In this invention, the outer edge
portion of the solid polymer electrolyte membrane 1 is preferably
sandwiched and pressed by the separators 22 to increase the sealing
properties, thereby preventing gases from being mixed. On one side
of the electricity-generating region of the solid polymer
electrolyte membrane 1 is disposed the anode 23 and on another side
thereof is disposed the cathode 24. Further, a carbon fiber
diffusion layer 25 is disposed on each of the anode 23 and the
cathode 24 to diffuse the fuel gas or the oxidant gas. In the fuel
cell shown in FIG. 2, the sealing frames 21 are disposed on the
outer edge portion of each separator 22. To obtain a sufficient
gas-sealing properties, it is preferable that the
non-electricity-generating region of the solid polymer electrolyte
membrane 1 is sandwiched between a couple of sealing frames 21 and
the moisture-proof layer 11 is disposed between the
non-electricity-generating region and the sealing frames 21.
[0030] A method for producing the solid polymer electrolyte
membrane of the present invention is not particularly limited. An
example of producing the solid polymer electrolyte membrane will be
described referring to FIGS. 3(a) and 3(b) below.
[0031] First, a resin in a melted state is extruded from a die 41
so that the base film 12 is formed by extrusion molding. Then, the
moisture-proof material is sprayed on the
non-electricity-generating region of the base film 12 and hardened
to provide the moisture-proof layer 11. Although the moisture-proof
material is sprayed while moving a spraying apparatus to prevent
the moisture-proof material from adhering to the
electricity-generating region 13 in FIG. 3(a), the moisture-proof
material may be sprayed on the entire base film 12 while masking
the electricity-generating region 13 with an iron plate or while
taping the electricity-generating region 13. A method for forming
the moisture-proof layer is not particularly limited and may be a
known method. The method is preferably selected from the group
consisting of coating methods, spray methods, dipping methods and
printing methods. After forming the moisture-proof layer 11, the
resultant membrane is taken up or winded by a take-up roller 42. In
the case of using a heat-setting type moisture-proof material, the
membrane is made to pass through an oven, etc. before taking-up. In
the case where a sufficient period of time is required to harden
the moisture-proof material, distance between the spraying
apparatus and the take-up roller 42 may be increased. Then, the
resulting membrane is subjected to punching or cutting, to produce
the solid polymer electrolyte membrane having a desired shape.
EXAMPLES
[0032] The present invention will be explained in further detail by
the following examples without intention of restricting the scope
of the present invention defined by the claims attached hereto.
[0033] A moisture-proof material shown in Table 1 was applied to an
outer edge portion of a base film under conditions shown in Table 2
to form a moisture-proof layer, whereby solid polymer electrolyte
membranes of Examples 1 to 4 were produced, respectively. The base
film was made of a perfluorinated sulfonic acid polymer represented
by the following formula, and had a thickness of 50 .mu.m and a
size of 50 mm.times.50 mm. Further, a solid polymer electrolyte
membrane of Comparative Example 1, where the moisture-proof layer
was not disposed, was produced. Incidentally, because a heat
resistance temperature of the base film was lower than recommended
hardening temperatures (140.degree. C. and 200.degree. C.) of the
moisture-proof materials used in Examples 3 and 4, the
moisture-proof materials were heat-hardened at a temperature of
100.degree. C., at which the base film was not deteriorated, in
Examples 3 and 4.
1TABLE 1 Properties and Composition of Moisture-Proof Material
Recommended Hardening Condition Resin Solvent Ex. 1 Room
Temperature Fluororesin Perfluorocarbon Ex. 2 Room Temperature
Fluororesin Butyl Acetate Ex. 3 140.degree. C. .times. 30 minutes
Fluororesin n-Heptane, Toluene and Isooctane Ex. 4 200.degree. C.
.times. 30 minutes Fluororesin and Methylethylketone Urethane Resin
and Toluene
[0034]
2TABLE 2 Conditions for Forming Moisture-Proof Layer Applying
Amount Drying and Hardening Applying Method (Solid State)
Conditions Ex. 1 Brushing of Two Times at 10 g/m.sup.2 Room
Interval of 5 minutes Temperature .times. 1 hour Ex. 2 Brushing of
Two Times at 10 g/m.sup.2 Room Interval of 5 minutes Temperature
.times. 1 hour Ex. 3 Spraying of 3 Round Trips 5.5 g/m.sup.2
100.degree. C. .times. 1 hour Ex. 4 Spraying of 3 Round Trips 6
g/m.sup.2 100.degree. C. .times. 1 hour
[0035] 1
[0036] Each of the solid polymer electrolyte membranes was
subjected to a moisture resistance test, and after heating them at
90.degree. C. for 200 hours, each membrane was subjected to a
sealing properties test. Results of the moisture resistance test
and the sealing properties test were shown in Tables 3 and 4,
respectively. Incidentally, the sealing properties test was carried
out by an apparatus shown in FIG. 4 as follows: a stack of an anode
23, a cathode 24, a carbon fiber diffusion layers 25 and a solid
polymer electrolyte membrane 1 was assembled with sealing frames 21
and jigs 31a and 31b corresponding to a separator; the resultant
assemble was soaked in water and applied a pressure by He gas
through a connector and a tube (not shown) disposed on an aperture
32 of the jig 31a; and gas leakage was evaluated by observing
bubbles generated between the jigs 31a and 31b and by a flow meter
disposed on the pressure-applying line.
3TABLE 3 Results of Moisture Resistance rest Surface of Solid
Polymer Electrolyte Membrane Surface of Applied After 1 hour After
1 hour Moisture-Proof Material at 30.degree. C., 90% RH at
90.degree. C., 90% RH Immediately Visual Visual After Applying
After Hardening Observation Dimension Observation Dimension Ex. 1
No Swell No Swell, Slightly a: +2% Slightly a: +2% Slightly
Extended Wrinkled b: 0% Wrinkled b: 0% Ex. 2 No Swell No Swell,
Slightly a: +4% Slightly a: +4% Slightly Extended Wrinkled b: 0%
Wrinkled b: 0% Ex. 3 -- Slightly Swelled Slightly a: +1% Slightly
a: +1% Swelled b: +1% Swelled b: +1% Ex. 4 -- Slightly Swelled
Extremely a: +1% Extremely a: +4% Wrinkled b: 0% Wrinkled b: +6%
Comp. -- -- Extremely a: +4% Extremely a: +10% Ex. 1 Wrinkled b:
-4% Wrinkled b: -4% The term "Swelled" means that the
moisture-proof material or the solid polymer electrolyte membrane
was entirely shape-changed with deflection. The term "Wrinkled"
means that the solid polymer electrolyte membrane was finely
shape-changed, not entirely. a: Vertical direction to drawing
direction b: Drawing direction
[0037]
4TABLE 4 Results of Sealing Properties Test Gas Leakage Ex. 1 Not
Observed at 200 kPa Ex. 2 Not Observed at 200 kPa Ex. 3 Not
Observed at 200 kPa Ex. 4 Observed at 150 kPa Comp. Ex. 1 Observed
at 100 kPa
[0038] As shown in Table 3, the solid polymer electrolyte membranes
of Examples 1 to 3 were improved with respect to the moisture
resistance as compared with the solid polymer electrolyte membrane
of Comparative Example 1. Although the moisture resistance of the
solid polymer electrolyte membrane of Example 4 was hardly improved
as compared with the solid polymer electrolyte membrane of
Comparative Example 1, this was because the moisture-proof material
was not sufficiently hardened at 100.degree. C. lower than the
recommended temperature of 200.degree. C.
[0039] As shown in Table 4, in the solid polymer electrolyte
membrane of Comparative Example 1, gas leakage was occurred by a
sealing pressure. As compared with this, the solid polymer
electrolyte membranes of Examples 1 to 4 had a sufficient sealing
properties for the sealing pressure.
[0040] As described in detail above, a solid polymer electrolyte
membrane of the present invention comprises a moisture-proof layer
to be excellent in moisture resistance and sealing properties. The
solid polymer electrolyte membrane is remarkably useful for a fuel
cell stack.
* * * * *